In general, display devices are electric and optical devices, which are used to transform electric signals into visual images so that a user can directly recognize information. Among the display devices, an LCD device is a display device utilizing optical characteristics of a liquid crystal. That is, the LCD device displays an image according as the arrangement of liquid crystal molecules is changed by applying electric field thereto.
When thin film transistors are employed for large-sized display devices, the gate resistance of the transistor should be small so as to prevent a delay of signals or a flickering of an image. As a metal having small resistance and large conductivity, copper (Cu) and aluminum (Al) can be exemplified. However, these metals are restricted in processing. In particular, copper has the lowest resistivity among various metals and so a development on processing utilizing copper attracts much concern. However, when copper is used for the processing, an adhesive strength thereof onto a substrate or onto an insulation layer is low and copper is liable to form a native oxide film thereon. In addition, when a copper wiring is employed for manufacturing a thin film transistor substrate, the diffusion of copper into a silicon (Si) substrate should be prevented and an adhesive strength onto the substrate also should be confirmed.
Accordingly, the development of a wiring material giving improved characteristics of a transistor and a good ohmic contact property of a device is continuously required.